This invention relates to an apparatus for measuring an optical characteristic of a sample using an integrating sphere, which is adopted in a spectral colorimeter.
In spectral calorimeters or optical characteristic measuring apparatus using an integrating sphere, there are cases of requiring both a spectral reflection coefficient including specular components from a sample (hereinafter, SCI spectral reflection coefficient) and a spectral reflection coefficient excluding specular components (hereinafter, SCE spectral reflection coefficient). For example, for computer color matching (CCM), the SCI data which are unlikely to be influenced by a surface state are often used. For color estimation, etc., the SCE data having a high correlation with visual sense are often used.
In a conventional d/8 optical system which diffusely illuminates a sample by an integrating sphere and receives a reflected light by a light receiving device disposed at 8.degree. with respect to a normal line to a sample surface, a trap aperture is formed at the position of a wall of the integrating sphere that corresponds to -8.degree. with respect to the normal line to the sample surface. This trap aperture is opened and closed to switch specular reflection light incident upon the light receiving device on and off.
FIG. 4 shows a conventional optical characteristic measuring apparatus. On an inner surface la of an integrating sphere 1 is applied with BaSO.sub.4 or the like material having a high diffusion coefficient and a high reflection coefficient. A beam of light from a light source 11 is introduced into the integrating sphere 1 through an aperture 16, undergoes a multiple reflection at the inner surface of the integrating sphere 1, and diffusely illuminates a sample 3 disposed at a sample aperture 2.
The light reflected by the sample 3 is introduced through an aperture 31 to a sample spectral device 30 via a receiving optical system 32. At the same time, a part of the light diffusely illuminating the sample 3 is taken by a light guide 41 and introduced to a monitoring spectral device 40. The reflection coefficient of the sample 3 is calculated based on the outputs of the sample spectral device 30 and the monitoring spectral device 40.
An optical axis 32a of the receiving optical system 32 is slanted by 8.degree. with respect to a normal line 2a of the surface of the sample 3 as shown in FIG. 4. On the other hand, a trap aperture 4a is formed at the position of a wall of the integrating sphere 1 which corresponds to a direction symmetrical to the optical axis 32a of the receiving optical system 32 with respect to the normal line 2a, i.e., along a direction at -8.degree. with respect to the normal line 2a. The trap aperture 4a is selectively closeable by a closing member 4' having a reflective inner surface. In the state that the surface of the sample 3 is smooth, the inner surface of the closing member 4' acts as a light source of the specular reflection light of the sample 3 to be incident upon the receiving optical system 32.
Accordingly, when the closing member 4' is removed as shown in FIG. 4, the SCE spectral reflection coefficient can be measured. On the other hand, when the closing member 4' is placed in the trap aperture 4a, the SCI spectral reflection coefficient can be measured.
However, the conventional apparatus requires a lot of time and labor for the measurement since it makes it necessary to open and close the closing member 4' each time the sample 3 is replaced. In addition, since the conventional apparatus requires such mechanical operation, the reliability of measurement result is inevitably reduced.